1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and more particularly to a high brightness nitride-based semiconductor light emitting device and a method of manufacturing the same, which forms an ohmic contact for a p-side electrode using an ion implantation process, thereby replacing a conventional transparent conductive layer of Ni/Au.
2. Description of the Related Art
In general, a nitride-based semiconductor is used for a light emitting diode for emitting light in a wavelength range of a blue light or a green light and usually comprises a semiconductor material with the formula AlxInyGa(1−x−y)N (where 0≦x≦1, 0≦y≦1, 0≦x+y≦1).
For the light emitting device generating a green light, a gallium nitride (GaN) semiconductor material with a large energy band gap of about 3.4 eV is used. Like the GaN semiconductor material, as the nitride-based semiconductor has a large energy band gap, there is a difficulty in achieving an ohmic contact with an electrode therein. More specifically, a contact resistance at a p-side electrode increases, causing a rise in operating voltage and the amount of heat. As for a method for providing the ohmic contact, various methods have been suggested. However, since an ohmic contact portion is provided as a primary light emitting plane, it is needed to satisfy a requirement of ensuring a transmission of light generated from an active layer through the light emitting plane. Thus, only a few methods could be restrictively adopted in practice as a method for lowering the contact resistance.
As to a conventional method satisfying the requirement, U.S. Pat. No. 5,563,422 entitled “Nitride gallium-based III-IV compound semiconductor device and method of producing the same,” which is assigned to Nichia Chemical Industry Limited, discloses a transparent electrode layer using a bi-layer of Ni/Au. FIG. 1 shows a light emitting device according to an embodiment of the disclosure.
As shown in FIG. 1, a nitride semiconductor light emitting device 10 of the prior art comprises an n-type GaN clad layer 13, a GaN/InGaN active layer 15 having a multi-well structure and a p-type GaN clad layer 17, which are sequentially formed on the substrate 11 in this order. In the nitride semiconductor light emitting device 10, a portion of the p-type GaN clad layer 17 and GaN/InGaN active layer 15 is removed to expose a portion of the n-type GaN clad layer 13. After forming an n-side electrode 19a on the n-type GaN clad layer 13 and a transparent electrode 18 of Ni/Au for providing the ohmic contact on the p-type GaN clad layer 17, a p-side bonding electrode 19b is prepared. The transparent electrode 18 is a translucent layer for lowering the contact resistance and can be formed through a deposition process of a bi-layer of Ni/Au and a subsequent annealing treatment.
It is desirable that the transparent electrode 18 is formed as thick as possible in order to improve current injection efficiency. However, since the transparent electrode 18 is formed of metallic materials, it may be difficult for the transparent electrode to have a desired transmittance. Even though a NiO layer of a relatively high translucency can be formed through the annealing treatment, this layer has a transmittance of merely 60%, so that light emitting efficiency can be deteriorated when thickening the transparent electrode. Thus, the transparent electrode should be limited to a thickness of 100 μm or less, causing a restriction in improving the current injection efficiency.
Further, even though the transparent electrode made of the metallic materials is formed to have an adequate thickness in consideration of a desired transmittance, it inevitably encounters some deterioration in brightness due to a limited transmittance of the transparent electrode.
Thus, there is a need in the art to provide a new light emitting device and a method of manufacturing the same, which can improve the contact resistance without deteriorating the brightness for a reduction in transmittance, unlike the conventional method using the transparent electrode.